Carboxy-functional dimer fatty acid-based reaction products and aqueous basecoat materials comprising said products

ABSTRACT

The present invention relates to a pigmented aqueous basecoat material comprising a carboxy-functional dimer fatty acid-based reaction product which is preparable by reaction of 
     (a) dimer fatty acids with
 
(b) at least one compound of the general structural formula (I)
 
     
       
         
         
             
             
         
       
     
     where R is a C 3  to C 6  alkylene radical and n is selected accordingly such that the polyether (b) possesses a number-average molecular weight of 120 to 6000 g/mol, components (a) and (b) are used in a molar ratio of at least 1/1 and the resulting reaction product possesses a number-average molecular weight of 1000 to 20 000 g/mol and an acid number of 10 to 120 mg KOH/g.

The present invention relates to innovative carboxy-functional, dimerfatty acid-based reaction products. It further relates to aqueousbasecoat materials which comprise the reaction products, and to the useof said reaction products in aqueous basecoat materials. It also relatesto a method for producing multicoat paint systems using aqueous basecoatmaterials, and also to the multicoat paint systems producible by meansof said method.

PRIOR ART

A multiplicity of methods are known for producing multicoat color and/oreffect paint systems (also called multicoat coatings or multiple-coatfinishes). The prior art discloses (cf., for example, German patentapplication DE 199 48 004 A1, page 17 line 37 to page 19 line 22, orGerman patent DE 100 43 405 C1, column 3 paragraph [0018], and column 8paragraph [0052] to column 9 paragraph [0057], in conjunction withcolumn 6 paragraph [0039] to column 8 paragraph [0050]), for example,the following method in which:

(1) a pigmented aqueous basecoat material is applied to a substrate,

(2) a polymer film is formed from the coating material applied in stage(1),

(3) a clearcoat material is applied to the resulting basecoat film, andthen

(4) the basecoat film is cured together with the clearcoat film.

This method is widely employed, for example, for the OEM finishing ofautomobiles, and also for the painting of metal and plastic ancillarycomponents. The current requirements imposed on theapplications-technological and esthetic properties of such paint systems(coatings) are immense.

One problem which arises again and again, and yet has still not beensatisfactorily solved by the prior art, is the incidence of what arecalled pinholes—i.e., the insufficient stability toward pinholes. Onsuccessive application of a number of coating materials—basecoat andclearcoat, for example—and in the absence of separate curing of each ofthe individual polymer films, there may be unwanted inclusions of air,solvent and/or moisture, which may become perceptible in the form ofbubbles beneath the surface of the overall paint system, and may breakopen in the course of the final curing. The holes that are formed in thepaint system as a result, also called pinholes, lead to adisadvantageous visual appearance. The amount of organic solvents and/orwater obtained as a result of the overall construction of basecoat filmand clearcoat film, and also the quantity of air introduced by theapplication procedure, are too great to be able to escape from themulticoat paint system completely within a final curing step without thegeneration of defects. The properties of the basecoat material, which isparticularly important in this context, and of the coating filmsproduced from it are determined in particular by the binders andadditives present in the basecoat material, examples being specificreaction products.

A further factor is that nowadays the replacement of coating materialsbased on organic solvents by aqueous coating materials is becoming evermore important in order to take account of the rising requirements forenvironmental friendliness.

Problem

The problem addressed by the present invention, therefore, was that ofproviding a reaction product which can be used to produce coatings whichno longer have the above-identified disadvantages of the prior art. Moreparticularly, the provision of a new reaction product and its use inaqueous basecoat materials ought to make it possible to provide coatingswhich exhibit outstanding stability toward pinholes and at the same timecan be produced by use of aqueous basecoat materials, in an eco-friendlyway.

Solution

The stated problems have been solved by a pigmented aqueous basecoatmaterial which comprises a carboxy-functional dimer fatty acid-basedreaction product which is preparable by reaction of

(a) dimer fatty acids with

(b) at least one compound of the general structural formula (I)

where R is a C₃ to C₆ alkylene radical and n is selected accordinglysuch that the polyether (b) possesses a number-average molecular weightof 120 to 6000 g/mol, components (a) and (b) are used in a molar ratioof at least 1/1 and the resulting reaction product possesses anumber-average molecular weight of 1000 to 20 000 g/mol and an acidnumber of 10 to 120 mg KOH/g.

The new basecoat material is also referred to below as basecoat materialof the invention. Preferred embodiments of the basecoat material of theinvention are apparent from the description which follows and from thedependent claims.

Likewise provided by the present invention is the reaction productitself and also the use of the reaction product in aqueous basecoatmaterials for improving the stability toward pinholes. The presentinvention relates not least to a method for producing a multicoat paintsystem on a substrate, and also to a multicoat paint system produced bysaid method.

Through the use of the reaction products of the invention, basecoatmaterials are obtained whose use in the production of coatings, moreparticularly multicoat paint systems, leads to outstanding stabilitytoward pinholes. At the same time a high-level environmental profile isensured. The reaction product of the invention and also the basecoatmaterial of the invention can be used in the OEM finishing sector,particularly in the automobile industry sector, and in the automotiverefinish sector.

Component (a)

The reaction product of the invention can be prepared using at least onedimer fatty acid (a).

Dimer fatty acids (which have also been known for a long time asdimerized fatty acids or dimer acids) are—generally and especially inthe context of the present invention—mixtures which are prepared byoligomerization of unsaturated fatty acids. They are preparable, forexample, by catalytic dimerization of unsaturated plant fatty acids,with starting materials used being more particularly unsaturated C₁₂- toC₂₂ fatty acids. The linking proceeds primarily according to theDiels-Alder type, and results, depending on the number and position ofthe double bonds in the fatty acids used for preparing the dimer fattyacids, in mixtures of primarily dimeric products, which between thecarboxyl groups have cycloaliphatic, linear-aliphatic, branchedaliphatic, and also C₆-aromatic hydrocarbon groups. Depending onmechanism and/or on optional subsequent hydrogenation, the aliphaticradicals may be saturated or unsaturated, and the fraction of aromaticgroups as well may vary. The radicals between the carboxylic acid groupsthen contain, for example, 24 to 44 carbon atoms. Fatty acids used forthe preparation are preferably those with 18 carbon atoms, meaning thatthe dimeric product has 36 carbon atoms. The radicals which join thecarboxyl groups of the dimer fatty acids preferably have no unsaturatedbonds and no aromatic hydrocarbon radicals.

For the purposes of the present invention, therefore, C₁₈ fatty acidsare used preferably in the preparation. Particular preference is givento using linolenic, linoleic and/or oleic acid.

Depending on the reaction regime, the above-designated oligomerizationproduces mixtures comprising principally dimeric molecules, but alsotrimeric molecules and also monomeric molecules and other byproducts.Purification is normally accomplished by distillation. Commercial dimerfatty acids contain generally at least 80 wt % of dimeric molecules, upto 19 wt % of trimeric molecules, and not more than 1 wt % of monomericmolecules and other byproducts.

Preference is given to using dimer fatty acids which consist to anextent of at least 90 wt %, preferably at least 95 wt %, more preferablyat least 98 wt % of dimeric fatty acid molecules.

In the sense of the present invention it is preferable to use dimerfatty acids which consist to an extent of at least 90 wt % of dimericmolecules, less than 5 wt % of trimeric molecules, and less than 5 wt %of monomeric molecules and other byproducts. Particular preference isgiven to using dimer fatty acids which consist to an extent of 95 to 98wt % of dimeric molecules, less than 5 wt % of trimeric molecules, andless than 1 wt % of monomeric molecules and other byproducts. Likewiseparticularly preferred is the use of dimer fatty acids which consist toan extent of at least 98 wt % of dimeric molecules, less than 1.5 wt %of trimeric molecules, and less than 0.5 wt % of monomeric molecules andother byproducts. Determining the fractions of monomeric, dimeric, andtrimeric molecules and also of other byproducts in the dimer fatty acidscan be accomplished by means of gas chromatography (GC), for example. Inthat case, prior to the GC analysis, the dimer fatty acids are convertedto the corresponding methyl esters by the boron trifluoride method (seeDIN EN ISO 5509) and then analyzed by means of GC.

A fundamental characteristic of “dimer fatty acids” for the purposes ofthe present invention is therefore that their preparation encompassesthe oligomerization of unsaturated fatty acids. This oligomerizationproduces primarily—that is, preferably to an extent of at least 80 wt %,more preferably at least 90 wt %, very preferably at least 95 wt %, andmore particularly at least 98 wt %—dimeric products. The fact,therefore, that the oligomerization produces predominantly dimericproducts which contain exactly two fatty acid molecules justifies thisnomenclature, which is in any case commonplace. An alternativeexpression for the relevant term “dimer fatty acids” therefore, is“mixture comprising dimerized fatty acids”.

The dimer fatty acids for use are available as commercial products.Examples include Radiacid 0970, Radiacid 0971, Radiacid 0972, Radiacid0975, Radiacid 0976, and Radiacid 0977 from Oleon, Pripol 1006, Pripol1009, Pripol 1012, and Pripol 1013 from Croda, Empol 1008, Empol 1061,and Empol 1062 from Cognis, and also Unidyme 10 and Unidyme TI fromArizona Chemical.

Component (b)

The reaction products of the invention may be prepared using at leastone compound (b) of the general structural formula (I)

where R is a C₃ to C₆ alkyl radical. The index n is to be selected ineach case such that the compound (b) possesses a number-averagemolecular weight of 120 to 6000 g/mol. It preferably possesses anumber-average molecular weight of 150 to 3500 g/mol, more preferably of180 to 2500 g/mol, and more particularly 200 to 2200 g/mol. Thenumber-average molecular weight may for example be 250 g/mol, 500 g/mol,or 1000 g/mol. However, a value of 2000 g/mol or 3000 g/mol is alsopossible. Unless explicitly indicated otherwise, the number-averagemolecular weight in the context of the present invention is determinedby means of vapor pressure osmosis. Measurement was carried out by meansof a vapor pressure osmometer (model 10.00 from Knauer) on concentrationseries of the component under investigation in toluene at 50° C., withbenzophenone as calibration substance for determination of theexperimental calibration constant of the instrument employed (inaccordance with E. Schröder, G. Müller, K.-F. Arndt, “Leitfaden derPolymercharakterisierung” [Introduction to polymer characterization],Akademie-Verlag, Berlin, pp. 47-54, 1982, in which benzil was used ascalibration substance).

As is known, and as already explained earlier on above, thenumber-average molecular weight is always a statistical average value.The same, then, must also be true of the parameter n as per formula (I).The structural properties of the compound (b) that require explanationin this context may be represented as follows. A compound (b) istherefore mixtures of molecules with different sizes. At least aportion, or all, of these molecules are distinguished by a sequence ofidentical or different monomer units (as a reacted form of monomers). Acompound (b) or the corresponding molecule mixture therefore inprinciple comprises molecules which comprise a plurality of (that is, atleast two) identical or different monomer units. It will be appreciatedthat in the mixture there may also, proportionally, be the monomersthemselves, in other words in their unreacted form. This is the reasonalone, as is known, for the preparation reaction—that is, in particular,combination of monomers—that in general does not proceed with molecularuniformity. Whereas a defined monomer can be assigned a discretemolecular weight, a compound (b), therefore, is a mixture of moleculeswhich differ in their molecular weights. A compound (b), therefore,cannot be described by a discrete molecular weight, but instead is thusalways assigned average molecular weights, such as the number-averagemolecular weight stated above, for example. This principle is familiarto the skilled person from polymers, for example. Polymers as well arealways mixtures of different molecules.

Compound (b) is therefore understood for the purposes of the presentinvention to be a mixture of molecules, the mixture comprising moleculeswhich are distinguished by a sequence of identical or different monomerunits. This means, therefore, that the parameter n in the formula (I)given above for the compound (b) is in any case greater than 1.0.Preferably n is at least 1.5, more particularly at least 2.0, morepreferably at least 3.0. With preference, therefore, the compound (b) isan oligo-ether or a polyether. In the preferred embodiments (forexample, for n being at least 3), indeed, there are on average at leastthree monomers linked, and on average the molecules present in themixture have at least two ether bonds. In this preferred case,therefore, it is already possible to refer to a polymeric, or at leastoligomeric, character.

In the compound (b) which can be used in accordance with the inventionit is possible for all n radicals R to be identical. It is likewise alsopossible, however, for different kinds of radicals R to be present.Preferably all the radicals R are identical.

R is preferably a C₄ alkylene radical. More preferably it is atetramethylene radical.

With very particular preference the polyether for use in accordance withthe invention is a linear polytetrahydrofuran which on average isdiolic.

The Reaction Product

There are no peculiarities to the preparation of the reaction product ofthe invention. Components (a) and (b) are linked to one another viacommon-knowledge esterification. Accordingly, the carboxyl groups ofcomponent (a) are reacted with the hydroxyl groups of component (b). Thereaction may take place, for example, in bulk or in solution withtypical organic solvents at temperatures from, for example, 50° C. to300° C. It is of course also possible for typical catalysts to beemployed, such as sulfuric acid, sulfonic acids and/or tetraalkyltitanates, zinc and/or tin alkoxylates, dialkyltin oxides such asdi-n-butyltin oxide, for example, or organic salts of the dialkyltinoxides. Customarily, a water separator is also used, in order to collectthe water formed in the case of condensation reactions.

The components (a) and (b) here are used in a molar ratio of at least1/1, preferably 1/1 to 5/1, more preferably of 1.1/1 to 3/1, morepreferably still of 1.1/1 to 1.9/1, very particularly advantageously of1.1/1 to 1.8/1 and in a very particularly preferred embodiment of 1.2/1to 1.5/1. The molar amount of the dimer fatty acids (a) used istherefore at least equal to the molar amount of compound (b) used.

As a result of the molar ratio of components (a) and (b), the reactionproduct of the invention is, on average in any case, carboxy-functional.The acid number of the reaction product is from 10 to 120 mg KOH/g,preferably 12 to 80 mg KOH/g, especially preferably 14 to 60 mg KOH/gand very preferably 15 to 50 mg KOH/g. The acid number is determined inaccordance with DIN 53402. If reference is made in the context of thepresent invention to an official standard, this of course means theversion of the standard that was current on the filing date, or, if nocurrent version exists at that date, then the last current version.

The resulting reaction product possesses a number-average molecularweight of 1000 to 20 000 g/mol, preferably 1500 to 15 000 g/mol, verypreferably 2000 to 12 000 g/mol and more particularly 2500 to 10 000g/mol.

As examples of embodiments of the reaction products of the inventionthat are preferred in this sense, mention may be made of the followingparticularly preferred embodiments:

-   a) In one particularly preferred embodiment of the reaction product    of the invention, the dimer fatty acid is prepared from linolenic,    linoeic and/or oleic acid and consists to an extent of at least 98    wt % of dimeric molecules, less than 1.5 wt % of trimeric molecules,    and less than 0.5 wt % of monomeric molecules and other byproducts.-   b) In another particularly preferred embodiment of the reaction    product of the invention, the compound (b) for use in accordance    with the invention is polytetrahydrofuran and also possesses a    number-average molecular weight of 180 to 2500 g/mol.-   c) In another particularly preferred embodiment of the reaction    product of the invention, components (a) and (b) are used in a molar    ratio of 1.2/1 to 2/1.-   d) In another particularly preferred embodiment of the reaction    product of the invention, said product possesses an acid number of    15 to 50 mg KOH/g.-   e) In another particularly preferred embodiment of the reaction    product of the invention, said product possesses a number-average    molecular weight of 2500 to 10 000 g/mol.

As a further example of embodiments of the reaction products of theinvention that are preferred in this sense, mention may be made of thosewhich realize all of the features indicated under a) to e) incombination.

The Pigmented Aqueous Basecoat Material

The present invention further relates to a pigmented aqueous basecoatmaterial which comprises at least one reaction product of the invention.All of the preferred embodiments stated above with regard to thereaction product also, of course, apply in respect of the basecoatmaterial comprising the reaction product.

A basecoat material is a color-imparting intermediate coating materialthat is used in automotive finishing and general industrial painting.This basecoat material is generally applied to a metallic or plasticssubstrate which has been pretreated with a baked (fully cured) surfaceror primer-surfacer, or else, occasionally, is applied directly to theplastics substrate. Substrates used may also include existing paintsystems, which may optionally require pretreatment as well (by abrading,for example). It has now become entirely customary to apply more thanone basecoat film. Accordingly, in such a case, a first basecoat filmconstitutes the substrate for a second such film. A particularpossibility in this context, instead of application to a coat of a bakedsurfacer, is to apply the first basecoat material directly to a metalsubstrate provided with a cured electrocoat, and to apply the secondbasecoat material directly to the first basecoat film, withoutseparately curing the latter. To protect a basecoat film, or theuppermost basecoat film, from environmental effects in particular, atleast an additional clearcoat film is applied over it. This is generallydone in a wet-on-wet process—that is, the clearcoat material is appliedwithout the basecoat film being cured. Curing then takes place, finally,jointly. It is now also widespread practice to produce only one basecoatfilm on a cured electrocoat film, then to apply a clearcoat material,and then to cure these two films jointly.

The sum total of the weight-percentage fractions, based on the totalweight of the pigmented aqueous basecoat material, of all reactionproducts of the invention is preferably 0.1 to 30 wt %, more preferably1 to 20 wt %, and very preferably 1.5 to 15 wt % or even 2 to 12 wt %.

Where the amount of the reaction product of the invention is below 0.1wt %, it may be possible that no further improvement in stability withrespect to pinholes is achieved. Where the amount is more than 30 wt %,there may in certain circumstances be disadvantages, such asincompatibility of said reaction product in the basecoat material, forexample. Such incompatibility may be manifested, for example, in unevenleveling and also in floating or settling.

In the case of a possible particularization to basecoat materialscomprising preferred reaction products in a specific proportional range,the following applies. The reaction products which do not fall withinthe preferred group may of course still be present in the basecoatmaterial. In that case the specific proportional range applies only tothe preferred group of reaction products. It is preferred nonethelessfor the total proportion of reaction products, consisting of reactionproducts of the preferred group and reaction products which are not partof the preferred group, to be subject likewise to the specificproportional range.

In the case of restriction to a proportional range of 1.5 to 15 wt % andto a preferred group of reaction products, therefore, this proportionalrange evidently applies initially only to the preferred group ofreaction products. In that case, however, it would be preferable forthere to be likewise from 1.5 to 15 wt % in total present of alloriginally encompassed reaction products, consisting of reactionproducts from the preferred group and reaction products which do notform part of the preferred group. If, therefore, 5 wt % of reactionproducts of the preferred group are used, not more than 10 wt % of thereaction products of the nonpreferred group may be used.

The stated principle is valid, for the purposes of the presentinvention, for all stated components of the basecoat material and fortheir proportional ranges—for example, for the pigments, for thepolyurethane resins as binders, or else for the crosslinking agents suchas melamine resins.

The basecoat materials used in accordance with the invention comprisecolor and/or effect pigments. Such color pigments and effect pigmentsare known to those skilled in the art and are described, for example, inRömpp-Lexikon Lacke und Druckfarben, Georg Thieme Verlag, Stuttgart,N.Y., 1998, pages 176 and 451. The fraction of the pigments may besituated for example in the range from 1 to 40 wt %, preferably 2 to 30wt %, more preferably 3 to 25 wt %, based on the total weight of thepigmented aqueous basecoat material.

Preferred basecoat materials in the context of the present invention arethose which comprise, as binders, polymers curable physically,thermally, or both thermally and with actinic radiation. A “binder” inthe context of the present invention and in accordance with relevant DINEN ISO 4618 is the nonvolatile component of a coating composition,without pigments and fillers. Specific binders, accordingly, include,for example, typical coatings additives, the reaction product of theinvention, or typical crosslinking agents described later on below, evenif the expression is used primarily below in relation to particularpolymers curable physically, thermally, or both thermally and withactinic radiation, as for example particular polyurethane resins.

Besides the reaction product of the invention, the pigmented aqueousbasecoat materials of the invention more preferably comprise at leastone polyurethane resin as binder. Coating materials of this kindcomprising polyurethane resins may likewise customarily be curedphysically, thermally, or both thermally and with actinic radiation.

In the context of the present invention, the term “physical curing”means the formation of a film through loss of solvent from polymersolutions or polymer dispersions. Typically, no crosslinking agents arenecessary for this curing.

In the context of the present invention, the term “thermal curing” meansthe heat-initiated crosslinking of a coating film, with either aseparate crosslinking agent or else self-crosslinking binders beingemployed in the parent coating material. The crosslinking agent containsreactive functional groups which are complementary to the reactivefunctional groups present in the binders. This is commonly referred toby those in the art as external crosslinking. Where the complementaryreactive functional groups or autoreactive functional groups—that is,groups which react with groups of the same kind—are already present inthe binder molecules, the binders present are self-crosslinking.Examples of suitable complementary reactive functional groups andautoreactive functional groups are known from German patent applicationDE 199 30 665 A1, page 7 line 28 to page 9 line 24.

For the purposes of the present invention, actinic radiation meanselectromagnetic radiation such as near infrared (NIR), UV radiation,more particularly UV radiation, and particulate radiation such aselectron radiation. Curing by UV radiation is commonly initiated byradical or cationic photoinitiators. Where thermal curing and curingwith actinic light are employed in unison, the term “dual cure” is alsoused.

In the present invention preference is given both to basecoat materialswhich cure physically and to basecoat materials which cure thermally orboth thermally and with actinic radiation, i.e., by “dual cure”.

Preferred thermally curing basecoat materials are those which compriseas binder a polyurethane resin, preferably a hydroxyl-containingpolyurethane resin, and as crosslinking agent an aminoplast resin or ablocked or nonblocked polyisocyanate, preferably an aminoplast resin.Among the aminoplast resins, melamine resins are preferred.

The sum total of the weight-percentage fractions, based on the totalweight of the pigmented aqueous basecoat material, of all crosslinkingagents, preferably aminoplast resins and/or blocked and/or nonblockedpolyisocyanates, more particularly preferably melamine resins, ispreferably 1 to 20 wt %, more preferably 1.5 to 17.5 wt %, and verypreferably 2 to 15 wt % or even 2.5 to 10 wt %.

The polyurethane resin preferably present may be ionically and/ornonionically hydrophilically stabilized. In preferred embodiments of thepresent invention the polyurethane resin is ionically hydrophilicallystabilized. The preferred polyurethane resins are linear or containinstances of branching. The polyurethane resin is more preferably one inwhose presence olefinically unsaturated monomers have been polymerized.This polyurethane resin may be present alongside the polymer originatingfrom the polymerization of the olefinically unsaturated monomers,without these polymers being bonded covalently to one another. Equally,however, the polyurethane resin may also be bonded covalently to thepolymer originating from the polymerization of the olefinicallyunsaturated monomers. The olefinically unsaturated monomers arepreferably monomers containing acrylate groups and/or methacrylategroups. It is likewise preferred for the monomers containing acrylateand/or methacrylate groups to be used in combination with otherolefinically unsaturated compounds which contain no acrylate ormethacrylate groups. Olefinically unsaturated monomers attached to thepolyurethane resin are more preferably monomers containing acrylategroups or methacrylate groups, thereby producing polyurethane(meth)acrylates. Very preferably the polyurethane resin is apolyurethane (meth)acrylate. The polyurethane resin present withpreference is curable physically, thermally, or both thermally and withactinic radiation. More particularly it is curable either thermally orboth thermally and with actinic radiation. With particular preferencethe polyurethane resin comprises reactive functional groups throughwhich external crosslinking is possible.

Suitable saturated or unsaturated polyurethane resins are described, forexample, in

-   -   German patent application DE 199 14 896 A1, column 1, lines 29        to 49 and column 4, line 23 to column 11, line 5,    -   German patent application DE 199 48 004 A1, page 4, line 19 to        page 13, line 48,    -   European patent application EP 0 228 003 A1, page 3, line 24 to        page 5, line 40,    -   European patent application EP 0 634 431 A1, page 3, line 38 to        page 8, line 9, or    -   international patent application WO 92/15405, page 2, line 35 to        page 10, line 32.

The polyurethane resin is prepared using preferably the aliphatic,cycloaliphatic, aliphatic-cycloaliphatic, aromatic, aliphatic-aromaticand/or cycloaliphatic-aromatic polyisocyanates that are known to theskilled person.

As alcohol component for preparing the polyurethane resins, preferenceis given to using the saturated and unsaturated polyols of relativelyhigh molecular mass and of low molecular mass, and also, optionally,monoalcohols, in minor amounts, that are known to the skilled person.Low molecular mass polyols used are more particularly diols and, inminor amounts, triols, for introducing instances of branching. Examplesof suitable polyols of relatively high molecular mass are saturated orolefinically unsaturated polyester polyols and/or polyether polyols.Relatively high molecular mass polyols are more particularly polyesterpolyols, especially those having a number-average molecular weight of400 to 5000 g/mol.

For hydrophilic stabilization and/or for increasing the dispersibilityin aqueous medium, the polyurethane resin preferably present may containparticular ionic groups and/or groups which can be converted into ionicgroups (potentially ionic groups). Polyurethane resins of this kind arereferred to in the context of the present invention as ionicallyhydrophilically stabilized polyurethane resins. Likewise present may benonionic hydrophilically modifying groups. Preferred, however, are theionically hydrophilically stabilized polyurethanes. In more preciseterms, the modifying groups are alternatively

-   -   functional groups which can be converted to cations by        neutralizing agents and/or quaternizing agents, and/or cationic        groups (cationic modification) or    -   functional groups which can be converted to anions by        neutralizing agents, and/or anionic groups (anionic        modification)        and/or    -   nonionic hydrophilic groups (nonionic modification).

As the skilled person is aware, the functional groups for cationicmodification are, for example, primary, secondary and/or tertiary aminogroups, secondary sulfide groups and/or tertiary phosphine groups, moreparticularly tertiary amino groups and secondary sulfide groups(functional groups which can be converted to cationic groups byneutralizing agents and/or quaternizing agents). Mention should also bemade of the cationic groups—groups prepared from the aforementionedfunctional groups using neutralizing agents and/or quaternizing agentsknown to those skilled in the art—such as primary, secondary, tertiaryand/or quaternary ammonium groups, tertiary sulfonium groups and/orquaternary phosphonium groups, more particularly quaternary ammoniumgroups and tertiary sulfonium groups.

As is well known, the functional groups for anionic modification are,for example, carboxylic acid, sulfonic acid and/or phosphonic acidgroups, more particularly carboxylic acid groups (functional groupswhich can be converted to anionic groups by neutralizing agents), andalso anionic groups—groups prepared from the aforementioned functionalgroups using neutralizing agents known to the skilled person—such ascarboxylate, sulfonate and/or phosphonate groups.

The functional groups for nonionic hydrophilic modification arepreferably poly(oxyalkylene) groups, more particularly poly(oxyethylene)groups.

The ionically hydrophilic modifications can be introduced into thepolyurethane resin through monomers which contain the (potentially)ionic groups. The nonionic modifications are introduced, for example,through the incorporation of poly(ethylene) oxide polymers as lateral orterminal groups in the polyurethane molecules. The hydrophilicmodifications are introduced, for example, via compounds which containat least one group reactive toward isocyanate groups, preferably atleast one hydroxyl group. The ionic modification can be introduced usingmonomers which, as well as the modifying groups, contain at least onehydroxyl group. To introduce the nonionic modifications, preference isgiven to using the polyether diols and/or alkoxypoly(oxyalkylene)alcohols known to those skilled in the art.

The polyurethane resin may preferably be a graft polymer. Moreparticularly it is a polyurethane resin grafted with olefinicallyunsaturated compounds, preferably olefinically unsaturated monomers. Inthis case, then, the polyurethane is grafted, for example, with sidegroups and/or side chains that are based on olefinically unsaturatedmonomers. These are more particularly side chains based onpoly(meth)acrylates. Poly(meth)acrylates for the purposes of the presentinvention are polymers or polymeric radicals which comprise monomerscontaining acrylate and/or methacrylate groups, and preferably consistof monomers containing acrylate groups and/or methacrylate groups. Sidechains based on poly(meth)acrylates are understood to be side chainswhich are constructed during the graft polymerization, using monomerscontaining (meth)acrylate groups. In the graft polymerization,preference here is given to using more than 50 mol %, more particularlymore than 75 mol %, especially 100 mol %, based on the total amount ofthe monomers used in the graft polymerization, of monomers containing(meth)acrylate groups.

The side chains described are introduced into the polymer preferablyafter the preparation of a primary polyurethane resin dispersion. Inthis case the polyurethane resin present in the primary dispersion maycontain lateral and/or terminal olefinically unsaturated groups viawhich, then, the graft polymerization with the olefinically unsaturatedcompounds proceeds. The polyurethane resin for grafting may therefore bean unsaturated polyurethane resin (A). The graft polymerization is inthat case a radical polymerization of olefinically unsaturatedreactants. Also possible, for example, is for the olefinicallyunsaturated compounds used for the graft polymerization to contain atleast one hydroxyl group. In that case it is also possible first forthere to be attachment of the olefinically unsaturated compounds viathese hydroxyl groups through reaction with free isocyanate groups ofthe polyurethane resin. This attachment takes place instead of or inaddition to the radical reaction of the olefinically unsaturatedcompounds with the lateral and/or terminal olefinically unsaturatedgroups optionally present in the polyurethane resin. This is thenfollowed again by the graft polymerization via radical polymerization,as described earlier on above. The result in any case is polyurethaneresins grafted with olefinically unsaturated compounds, preferablyolefinically unsaturated monomers.

As olefinically unsaturated compounds with which the polyurethane resin(A) is preferably grafted it is possible to use virtually all radicallypolymerizable, olefinically unsaturated, and organic monomers which areavailable to the skilled person for these purposes. A number ofpreferred monomer classes may be specified by way of example:

-   -   hydroxyalkyl esters of (meth)acrylic acid or of other        alpha,beta-ethylenically unsaturated carboxylic acids,    -   (meth)acrylic acid alkyl and/or cycloalkyl esters having up to        20 carbon atoms in the alkyl radical,    -   ethylenically unsaturated monomers comprising at least one acid        group, more particularly exactly one carboxyl group, such as        (meth)acrylic acid, for example,    -   vinyl esters of monocarboxylic acids which are branched in        alpha-position and have 5 to 18 carbon atoms,    -   reaction products of (meth)acrylic acid with the glycidyl ester        of a monocarboxylic acid which is branched in alpha-position and        has 5 to 18 carbon atoms,    -   further ethylenically unsaturated monomers such as olefins        (ethylene for example), (meth)acrylamides, vinylaromatic        hydrocarbons (styrene for example), vinyl compounds such as        vinyl chloride and/or vinyl ethers such as ethyl vinyl ether.

Used with preference are monomers containing (meth)acrylate groups, andso the side chains attached by grafting are poly(meth)acrylate-basedside chains.

The lateral and/or terminal olefinically unsaturated groups in thepolyurethane resin, via which the graft polymerization with theolefinically unsaturated compounds can proceed, are introduced into thepolyurethane resin preferably via particular monomers. These particularmonomers, in addition to an olefinically unsaturated group, alsoinclude, for example, at least one group that is reactive towardisocyanate groups. Preferred are hydroxyl groups and also primary andsecondary amino groups. Especially preferred are hydroxyl groups.

The monomers described through which the lateral and/or terminalolefinically unsaturated groups may be introduced into the polyurethaneresin may also, of course, be employed without the polyurethane resinbeing additionally grafted thereafter with olefinically unsaturatedcompounds. It is preferred, however, for the polyurethane resin to begrafted with olefinically unsaturated compounds.

The polyurethane resin preferably present may be a self-crosslinkingand/or externally crosslinking binder. The polyurethane resin preferablycomprises reactive functional groups through which external crosslinkingis possible. In that case there is preferably at least one crosslinkingagent in the pigmented aqueous basecoat material. The reactivefunctional groups through which external crosslinking is possible aremore particularly hydroxyl groups. With particular advantage it ispossible, for the purposes of the method of the invention, to usepolyhydroxy-functional polyurethane resins. This means that thepolyurethane resin contains on average more than one hydroxyl group permolecule.

The polyurethane resin is prepared by the customary methods of polymerchemistry. This means, for example, the polymerization ofpolyisocyanates and polyols to polyurethanes, and the graftpolymerization that preferably then follows with olefinicallyunsaturated compounds. These methods are known to the skilled person andcan be adapted individually. Exemplary preparation processes andreaction conditions can be found in European patent EP 0521 928 B1, page2, line 57 to page 8, line 16.

The polyurethane resin preferably present preferably possesses anumber-average molecular weight of 200 to 30 000 g/mol, more preferablyof 2000 to 20 000 g/mol. It further possesses, for example, a hydroxylnumber of 0 to 250 mg KOH/g, but more particularly from 20 to 150 mgKOH/g. The acid number of the polyurethane resin is preferably 5 to 200mg KOH/g, more particularly 10 to 40 mg KOH/g. The hydroxyl number isdetermined in the context of the present invention in accordance withDIN 53240, the acid number in accordance with DIN 53402.

The polyurethane resin content is preferably between 5 and 80 wt %, morepreferably between 8 and 70 wt %, and very preferably between 10 and 60wt %, based in each case on the film-forming solids of the basecoatmaterial.

By film-forming solids, corresponding ultimately to the binder fraction,is meant the nonvolatile weight fraction of the basecoat material,without pigments and, where appropriate, fillers. The film-formingsolids can be determined as follows: A sample of the pigmented aqueousbasecoat material (approximately 1 g) is admixed with 50 to 100 timesthe amount of tetrahydrofuran and then stirred for around 10 minutes.The insoluble pigments and any fillers are then removed by filtrationand the residue is rinsed with a little THF, the THF being removed fromthe resulting filtrate on a rotary evaporator. The residue of thefiltrate is dried at 120° C. for two hours and the resultingfilm-forming solids are obtained by weighing.

The sum total of the weight-percentage fractions, based on the totalweight of the pigmented aqueous basecoat material, of all polyurethaneresins is preferably 2 to 40 wt %, more preferably 2.5 to 30 wt %, andvery preferably 3 to 20 wt %.

The pigmented aqueous basecoat material to be used may further compriseat least one polyester different from the reaction products of theinvention, more particularly a polyester having a number-averagemolecular weight of 400 to 5000 g/mol, as binder. Such polyesters aredescribed for example in DE 4009858 in column 6, line 53 to column 7,line 61 and column 10, line 24 to column 13, line 3.

There is preferably also a thickener present. Suitable thickeners areinorganic thickeners from the group of the sheet silicates. As well asthe inorganic thickeners, however, it is also possible to use one ormore organic thickeners. These are preferably selected from the groupconsisting of (meth)acrylic acid-(meth)acrylate copolymer thickeners,for example the commercial product Rheovis AS S130 (BASF), and ofpolyurethane thickeners, for example the commercial product Rheovis PU1250 (BASF). The thickeners used are different from the binders used.

Furthermore, the pigmented aqueous basecoat material may furthercomprise at least one adjuvant. Examples of such adjuvants are saltswhich can be decomposed thermally without residue or substantiallywithout residue, resins as binders that are curable physically,thermally and/or with actinic radiation and are different frompolyurethane resins, further crosslinking agents, organic solvents,reactive diluents, transparent pigments, fillers, molecularly disperselysoluble dyes, nanoparticles, light stabilizers, antioxidants, deaeratingagents, emulsifiers, slip additives, polymerization inhibitors,initiators of radical polymerizations, adhesion promoters, flow controlagents, film-forming assistants, sag control agents (SCAs), flameretardants, corrosion inhibitors, waxes, siccatives, biocides, andflatting agents.

Suitable adjuvants of the aforementioned kind are known, for example,from

-   -   German patent application DE 199 48 004 A1, page 14, line 4, to        page 17, line 5,    -   German patent DE 100 43 405 C1 column 5, paragraphs [0031] to        [0033].

They are used in the customary and known amounts.

The solids content of the basecoat materials of the invention may varyaccording to the requirements of the case in hand. The solids content isguided primarily by the viscosity required for application, moreparticularly for spray application, and so may be adjusted by theskilled person on the basis of his or her general art knowledge,optionally with assistance from a few exploratory tests.

The solids content of the basecoat materials is preferably 5 to 70 wt %,more preferably 8 to 60 wt %, and very preferably 12 to 55 wt %.

By solids content (nonvolatile fraction) is meant that weight fractionwhich remains as a residue on evaporation under specified conditions. Inthe present application, the solids content, unless explicitly indicatedotherwise, is determined in accordance with DIN EN ISO 3251. This isdone by evaporating the basecoat material at 130° C. for 60 minutes.

Unless indicated otherwise, this test method is likewise employed inorder to determine, for example, the fraction of various components ofthe basecoat material as a proportion of the total weight of thebasecoat material. Thus, for example, the solids of a dispersion of apolyurethane resin which is to be added to the basecoat material may bedetermined correspondingly in order to ascertain the fraction of thispolyurethane resin as a proportion of the overall composition.

The basecoat material of the invention is aqueous. The expression“aqueous” is known in this context to the skilled person. The phraserefers in principle to a basecoat material which is not basedexclusively on organic solvents, i.e., does not contain exclusivelyorganic-based solvents as its solvents but instead, in contrast,includes a significant fraction of water as solvent. “Aqueous” for thepurposes of the present invention should preferably be understood tomean that the coating composition in question, more particularly thebasecoat material, has a water fraction of at least 40 wt %, preferablyat least 50 wt %, very preferably at least 60 wt %, based in each caseon the total amount of the solvents present (i.e., water and organicsolvents). Preferably in turn, the water fraction is 40 to 90 wt %, moreparticularly 50 to 80 wt %, very preferably 60 to 75 wt %, based in eachcase on the total amount of the solvents present.

The basecoat materials employed in accordance with the invention may beproduced using the mixing assemblies and mixing techniques that arecustomary and known for producing basecoat materials.

The Method of the Invention and the Multicoat Paint System of theInvention

A further aspect of the present invention is a method for producing amulticoat paint system, where

(1) a pigmented aqueous basecoat material is applied to a substrate,

(2) a polymer film is formed from the coating material applied in stage(1),

(3) a clearcoat material is applied to the resulting basecoat film, andthen

(4) the basecoat film is cured together with the clearcoat film,

which comprises using in stage (1) a pigmented aqueous basecoat materialwhich comprises at least one reaction product of the invention. All ofthe above observations relating to the reaction product of the inventionand to the pigmented aqueous basecoat material are also valid in respectof the method of the invention. This is true more particularly also ofall preferred, very preferred, and especially preferred features.

Said method is preferably used to produce multicoat color paint systems,effect paint systems, and color and effect paint systems.

The pigmented aqueous basecoat material used in accordance with theinvention is commonly applied to metallic or plastics substrates thathave been pretreated with surfacer or primer-surfacer. Said basecoatmaterial may optionally also be applied directly to the plasticssubstrate.

Where a metallic substrate is to be coated, it is preferably furthercoated with an electrocoat system before the surfacer or primer-surfaceris applied.

Where a plastics substrate is being coated, it is preferably alsopretreated before the surfacer or primer-surfacer is applied. Thetechniques most frequently employed for such pretreatment are those offlaming, plasma treatment, and corona discharge. Flaming is used withpreference.

Application of the pigmented aqueous basecoat material of the inventionto metallic substrates already coated, as described above, with curedelectrocoat systems and/or surfacers may take place in the filmthicknesses customary within the automobile industry, in the range, forexample, of 5 to 100 micrometers, preferably 5 to 60 micrometers. Thisis done using spray application methods, for example compressed airspraying, airless spraying, high-speed rotation, electrostatic sprayapplication (ESTA), alone or in conjunction with hot spray application,for example hot air spraying.

Following the application of the pigmented aqueous basecoat material, itcan be dried by known methods.

For example, (1-component) basecoat materials, which are preferred, canbe flashed at room temperature for 1 to 60 minutes and subsequentlydried, preferably at optionally slightly elevated temperatures of 30 to90° C. Flashing and drying in the context of the present invention meanthe evaporation of organic solvents and/or water, as a result of whichthe paint becomes drier but has not yet cured or not yet formed a fullycrosslinked coating film.

Then a commercial clearcoat material is applied, by likewise commonmethods, the film thicknesses again being within the customary ranges,for example 5 to 100 micrometers.

After the clearcoat material has been applied, it can be flashed at roomtemperature for 1 to 60 minutes, for example, and optionally dried. Theclearcoat material is then cured together with the applied pigmentedbasecoat material. In the course of these procedures, crosslinkingreactions occur, for example, to produce on a substrate a multicoatcolor and/or effect paint system of the invention. Curing takes placepreferably thermally at temperatures from 60 to 200° C. Thermally curingbasecoat materials are preferably those which comprise as additionalbinder a polyurethane resin and as crosslinking agent an aminoplastresin or a blocked or nonblocked polyisocyanate, preferably anaminoplast resin. Among the aminoplast resins, melamine resins arepreferred.

In one particular embodiment, the method for producing a multicoat paintsystem comprises the following steps:

producing a cured electrocoat film on the metallic substrate byelectrophoretic application of an electrocoat material to the substrateand subsequent curing of the electrocoat material,

producing (i) a basecoat film or (ii) a plurality of basecoat filmsdirectly following one another directly on the cured electrocoat film by(i) application of an aqueous basecoat material directly to theelectrocoat film, or (ii) directly successive application of two or morebasecoat materials to the electrocoat film,

producing a clearcoat film directly on (i) the basecoat film or (ii) theuppermost basecoat film, by application of a clearcoat material directlyto (i) one basecoat film or (ii) the uppermost basecoat film,

where (i) one basecoat material or (ii) at least one of the basecoatmaterials is a basecoat material of the invention,

joint curing of the basecoat film (i) or of the basecoat films (ii) andalso of the clearcoat film.

In the latter embodiment, then, in comparison to the above-describedstandard methods, there is no application and separate curing of acommonplace surfacer. Instead, all of the films applied to theelectrocoat film are cured jointly, thereby making the overall operationmuch more economical. Nevertheless, in this way, and particularlythrough the use of a basecoat material of the invention comprising areaction product of the invention, multicoat paint systems are producedwhich have virtually no pinholes and hence are particularly visuallyoutstanding. This is surprising in particular since with this method,within the concluding curing step, a particularly large quantity oforganic solvents and/or water must escape from the system (since,indeed, there is no separate curing of a surfacer film), thereby greatlyincreasing the fundamental susceptibility to formation of pinholes.

The application of a coating material directly to a substrate ordirectly to a previously produced coating film is understood as follows:The respective coating material is applied in such a way that thecoating film produced from it is disposed on the substrate (on the othercoating film) and is in direct contact with the substrate (with theother coating film). Between coating film and substrate (other coatingfilm), therefore, there is more particularly no other coat. Without thedetail “direct”, the applied coating film, while disposed on thesubstrate (the other film), need not necessarily be present in directcontact. More particularly, further coats may be disposed between them.In the context of the present invention, therefore, the following is thecase: In the absence of particularization as to “direct”, there isevidently no restriction to “direct”.

Plastics substrates are coated basically in the same way as metallicsubstrates. Here, however, in general, curing takes place atsignificantly lower temperatures, of 30 to 90° C. Preference istherefore given to the use of two-component clearcoat materials.Furthermore, in this context, preference is given to use of basecoatmaterials which comprise a polyurethane resin as binder, but nocrosslinker.

The method of the invention can be used to paint metallic andnonmetallic substrates, more particularly plastics substrates,preferably automobile bodies or components thereof.

The method of the invention can be used further for dual finishing inOEM finishing. This means that a substrate which has been coated bymeans of the method of the invention is painted for a second time,likewise by means of the method of the invention.

The invention relates further to multicoat paint systems which areproducible by the method described above. These multicoat paint systemsare to be referred to below as multicoat paint systems of the invention.

All of the above observations relating to the reaction product of theinvention and to the pigmented aqueous basecoat material are also validin respect of said multicoat paint system and of the method of theinvention. This is also true especially of all the preferred, morepreferred and most preferred features.

The multicoat paint systems of the invention are preferably multicoatcolor paint systems, effect paint systems, and color and effect paintsystems.

A further aspect of the invention relates to the method of theinvention, wherein said substrate from stage (1) is a multicoat paintsystem having defects. This substrate/multicoat paint system, whichpossesses defects, is therefore an original finish, which is to berepaired or completely recoated.

The method of the invention is suitable accordingly for repairingdefects on multicoat paint systems. Film defects are generally faults onand in the coating, usually named according to their shape or theirappearance. The skilled person is aware of a host of possible kinds ofsuch film defects. They are described for example in Römpp-Lexikon Lackeund Druckfarben, Georg Thieme Verlag, Stuttgart, N.Y., 1998, page 235,“Film defects”.

The multicoat paint systems produced by means of the method of theinvention may likewise have such defects. In one preferred embodiment ofthe method of the invention, therefore, the substrate from stage (1) isa multicoat paint system of the invention which exhibits defects.

These multicoat paint systems are produced preferably on automobilebodies or parts thereof, by means of the method of the invention,identified above, in the context of automotive OEM finishing. Where suchdefects occur directly after OEM finishing has taken place, they arerepaired immediately. The term “OEM automotive refinishing” is thereforealso used. Where only small defects require repair, only the “spot” isrepaired, and the entire body is not completely recoated (dual coating).The former process is called “spot repair”. The use of the method of theinvention for remedying defects on multicoat paint systems (originalfinishes) of the invention in OEM automotive refinishing, therefore, isparticularly preferred.

Where reference is made, in the context of the present invention, to theautomotive refinish segment, in other words when the repair of defectsis the topic, and the substrate specified is a multicoat paint systempossessing defects, this of course means that this substrate/multicoatpaint system with defects (original finish) is generally located on aplastic substrate or on a metallic substrate as described above.

So that the repaired site has no color difference from the rest of theoriginal finish, it is preferred for the aqueous basecoat material usedin stage (1) of the method of the invention for repairing defects to bethe same as that which was used to produce the substrate/multicoat paintsystem with defects (original finish).

The observations above concerning the polymer of the invention and theaqueous pigmented basecoat material therefore are also valid for theuse, under discussion, of the method of the invention for repairingdefects on a multicoat paint system. This is also true in particular ofall stated preferred, very preferred, and especially preferred features.It is additionally preferred for the multicoat paint systems of theinvention that are to be repaired to be multicoat color paint systems,effect paint systems, and color and effect paint systems.

The above-described defects on the multicoat paint system of theinvention can be repaired by means of the above-described method of theinvention. For this purpose, the surface to be repaired on the multicoatpaint system may initially be abraded. The abrading is preferablyperformed by partially sanding, or sanding off, only the basecoat andthe clearcoat from the original finish, but not sanding off the primerlayer and surfacer layer that are generally situated beneath them. Inthis way, during the refinish, there is no need in particular forrenewed application of specialty primers and primer-surfacers. This formof abrading has become established especially in the OEM automotiverefinishing segment, since here, in contrast to refinishing in aworkshop, generally speaking, defects occur only in the basecoat and/orclearcoat region, but do not, in particular, occur in the region of theunderlying surfacer and primer coats. Defects in the latter coats aremore likely to be encountered in the workshop refinish sector. Examplesinclude paint damage such as scratches, which are produced, for example,by mechanical effects and which often extend down to the substratesurface (metallic or plastic substrate).

After the abrading procedure, the pigmented aqueous basecoat material isapplied to the defect site in the original finish by pneumaticatomization. After the pigmented aqueous basecoat material has beenapplied, it can be dried by known methods. For example, the basecoatmaterial may be dried at room temperature for 1 to 60 minutes andsubsequently dried at optionally slightly elevated temperatures of 30 to80° C. Flashing and drying for the purposes of the present inventionmeans evaporation of organic solvents and/or water, whereby the coatingmaterial is as yet not fully cured. For the purposes of the presentinvention it is preferred for the basecoat material to comprise apolyurethane resin as binder and an aminoplast resin, preferably amelamine resin, as crosslinking agent. A commercial clearcoat materialis subsequently applied, by techniques that are likewise commonplace.Following application of the clearcoat material, it may be flashed offat room temperature for 1 to 60 minutes, for example, and optionallydried. The clearcoat material is then cured together with the appliedpigmented basecoat material.

In the case of so-called low-temperature baking, curing takes placepreferably at temperatures of 20 to 90° C. Preference here is given tousing two-component clearcoat materials. If, as described above, apolyurethane resin is used as further binder and an aminoplast resin isused as crosslinking agent, there is only slight crosslinking by theaminoplast resin in the basecoat film at these temperatures. Here, inaddition to its function as a curing agent, the aminoplast resin alsoserves for plasticizing and may assist pigment wetting. Besides theaminoplast resins, nonblocked isocyanates may also be used. Depending onthe nature of the isocyanate used, they crosslink at temperatures fromas low as 20° C.

In the case of what is called high-temperature baking, curing isaccomplished preferably at temperatures of 130 to 150° C. Here bothone-component and two-component clearcoat materials are used. If, asdescribed above, a polyurethane resin is used as further binder and anaminoplast resin is used as crosslinking agent, there is crosslinking bythe aminoplast resin in the basecoat film at these temperatures.

For repairing defects on multicoat paint systems, in other words whenthe substrate is an original finish with defects, preferably a multicoatpaint system of the invention that exhibits defects, the low-temperaturebaking is preferably employed.

A further aspect of the present invention is the use of the reactionproduct of the invention in pigmented aqueous basecoat materials forimproving the stability with respect to optical defects, moreparticularly pinholes.

The quality of the stability with respect to pinholes may be determinedin principle using the pinholing limit and also the number of pinholes.The pinholing limit and its determination may be described as follows:In the construction of a multicoat paint system, the film thickness of abasecoat film disposed beneath the clearcoat film is varied, and,moreover, this basecoat film is not baked separately, but is insteadbaked together with the clearcoat film. This coating film may be, forexample, a film disposed directly on the electrocoat film and/or a filmdisposed directly beneath the clearcoat film. It follows from theintroductory remarks that the tendency to form pinholes must increase asthe thickness of this film goes up, since correspondingly larger amountsof air, of organic solvents and/or of water are required to escape fromthe film. The film thickness of this film at which pinholes becomeapparent is referred to as the pinholing limit. The higher the pinholinglimit, the better, evidently, is the quality of the stability withrespect to pinholes. The number of pinholes as well is of course anexpression of the quality of the stability with respect to pinholes.

The invention is illustrated below using examples.

EXAMPLES Specification of Particular Components and Measurement Methods

Polyester 1 (P1):

Prepared in accordance with example D, column 16, lines 37 to 59 of DE4009858 A, using butyl glycol instead of butanol as organic solvent, thesolvents present thus being butyl glycol and water. The correspondingdispersion of the polyester has a solids content of 60 wt %.

Dimer Fatty Acid (a):

The dimer fatty acid used contains less than 1.5 wt % of trimericmolecules, 98 wt % of dimeric molecules, and less than 0.3 wt % of fattyacid (monomer). It is prepared on the basis of linolenic, linoleic, andoleic acid (Pripol™ 1012-LQ-(GD) (from Croda)).

Determination of the Number-Average Molecular Weight:

The number-average molecular weight was determined by means of vaporpressure osmosis. Measurement was effected using a vapor pressureosmometer (model 10.00 from Knauer) on concentration series of thecomponent under investigation in toluene at 50° C., with benzophenone ascalibration substance for determination of the experimental calibrationconstant of the instrument employed (in accordance with E. Schröder, G.Müller, K.-F. Arndt, “Leitfaden der Polymercharakterisierung”[Introduction to polymer characterization], Akademie-Verlag, Berlin, pp.47-54, 1982, in which, though, benzil was used as calibrationsubstance).

Production of Inventive Reaction Products (IR):

IR1:

In a 4 l stainless steel reactor equipped with anchor stirrer,thermometer, condenser, thermometer for overhead temperaturemeasurement, and water separator, 604.6 g of linear PolyTHF250 (fromBASF SE) with an OH number of 448.9 mg KOH/g (2.418 mol), 1818.5 g ofdimer fatty acid (3.139 mol), and 75.0 g of xylene were heated to 100°C. in the presence of 1.9 g of di-n-butyltin oxide (Axion® CS 2455, fromChemtura) (OH number determined according to DIN 53240). Heating wascontinued slowly until the onset of condensation. Then, at a maximumoverhead temperature of 85° C., heating was continued in steps up to186° C. The progress of the reaction was monitored by determination ofthe acid number. When an acid number of 38.1 mg KOH/g had been reached,remaining xylene was removed by distillation under reduced pressure.This gave a resin which was liquid at room temperature.

Gas chromatography found a xylene content of less than 0.1%.

The number-average molecular weight and the acid number of the polymerwere determined.

After cooling, the polyester was dissolved in butyl glycol (from BASFSE), as an 80% polymer solution.

Amount of condensate (water): 81.2 g

Acid number (polymer): 38.0 mg KOH/g

Number-average molecular weight (polymer): 2800 g/mol

Solids content (after dissolution) (60 min at 130° C.): 80.2%

Viscosity (80% strength in butyl glycol): 2110 mPas, (measured at 23° C.using a rotational viscometer from Brookfield, model CAP 2000+, spindle3, shear rate: 1000 s⁻¹)

IR2:

In a 4 l stainless steel reactor equipped with anchor stirrer,thermometer, condenser, and water separator, 1107.3 g of linearPolyTHF650 (from BASF SE) with an OH number of 172.6 mg KOH/g (1.704mol), 1315.8 g of dimer fatty acid (2.271 mol), and 75.0 g of xylenewere heated to 100° C. in the presence of 1.9 g of di-n-butyltin oxide(Axion® CS 2455, from Chemtura) (OH number determined according to DIN53240). Heating was continued slowly until the onset of condensation.Then, at a maximum overhead temperature of 85° C., heating was continuedin steps up to 200° C. The progress of the reaction was monitored bydetermination of the acid number. When an acid number of 28.8 mg KOH/ghad been reached, remaining xylene was removed by distillation underreduced pressure. This gave a resin which was liquid at roomtemperature.

Gas chromatography found a xylene content of less than 0.1%.

The number-average molecular weight and the acid number of the polymerwere determined.

After cooling, the polyester was dissolved in butyl glycol (from BASFSE), as an 80% polymer solution.

Amount of condensate (water): 60.7 g

Acid number (polymer): 28.5 mg KOH/g

Number-average molecular weight (polymer): 4000 g/mol

Solids content (after dissolution) (60 min at 130° C.): 80.4%

Viscosity (80% strength in butyl glycol): 2950 mPas, (measured at 23° C.using a rotational viscometer from Brookfield, model CAP 2000+, spindle3, shear rate: 1000 s⁻¹)

IR3:

In a 4 l stainless steel reactor equipped with anchor stirrer,thermometer, condenser, and water separator, 1373.6 g of linearPolyTHF1000 (from BASF SE) with an OH number of 111.0 mg KOH/g (1.359mol), 1049.4 g of dimer fatty acid (1.811 mol), and 75.0 g of xylenewere heated to 100° C. in the presence of 1.9 g of di-n-butyltin oxide(Axion® CS 2455, from Chemtura) (OH number determined according to DIN53240). Heating was continued slowly until the onset of condensation.Then, at a maximum overhead temperature of 85° C., heating was continuedin steps up to 190° C. The progress of the reaction was monitored bydetermination of the acid number. When an acid number of 22.2 mg KOH/ghad been reached, remaining xylene was removed by distillation underreduced pressure. This gave a resin which was liquid at roomtemperature.

Gas chromatography found a xylene content of less than 0.1%.

The number-average molecular weight and the acid number of the polymerwere determined.

After cooling, the polyester was dissolved in butyl glycol (from BASFSE), as an 80% polymer solution.

Amount of condensate (water): 47.0 g

Acid number (polymer): 22.2 mg KOH/g

Number-average molecular weight (polymer): 5200 g/mol

Solids content (after dissolution) (60 min at 130° C.): 80.3%

Viscosity (80% strength in butyl glycol): 4200 mPas, (measured at 23° C.using a rotational viscometer from Brookfield, model CAP 2000+, spindle3, shear rate: 1000 s⁻¹)

Production of Aqueous Basecoat Materials

Production of a Silver Comparative Waterborne Basecoat 1 (C1)

The components listed under “aqueous phase” in table A were stirredtogether in the order stated to form an aqueous mixture. In the nextstep an organic mixture was prepared from the components listed under“organic phase”. The organic mixture was added to the aqueous mixture.The combined mixture was then stirred for 10 minutes and adjusted, usingdeionized water and dimethylethanolamine, to a pH of 8 and to a sprayviscosity of 58 mPas under a shearing load of 1000 s⁻¹ as measured witha rotary viscometer (Rheomat RM 180 instrument from Mettler-Toledo) at23° C.

TABLE A Parts by Component weight Aqueous phase 3% Na—Mg phyllosilicatesolution 26 Deionized water 13.6 Butyl glycol 2.8 Polyurethane-modifiedpolyacrylate; 4.5 prepared as per page 7, line 55 to page 8, line 23 ofDE 4437535 A 50% strength by weight solution of 0.6 Rheovis PU 1250(BASF), rheological agent P1 3.2 TMDD (BASF) 0.3 melamine-formaldehyderesin (Cymel 203 4.1 from Cytec) 10% dimethylethanolamine in water 0.3polyurethane-based graft copolymer; 20.4 prepared as per page 19, line44 to page 20, line 21 of DE 19948004 A, solids content adjusted to 32.5wt % with deionized water TMDD (BASF) 1.6 3% strength by weight aqueousRheovis AS 3.9 S130 solution; rheological agent, available from BASFOrganic phase Mixture of two commercial aluminum 6.2 pigments, availablefrom Altana-Eckart Butyl glycol 7.5 P1 5

Production of an Inventive Waterborne Basecoat Material 1 (I1)

To produce the inventive waterborne basecoat material I1, a paint wasproduced as for the production of the comparative waterborne basecoatmaterial 1 (C1), using IR1, instead of the polyester P1, both in theaqueous phase and in the organic phase. IR1 here was used in dissolvedform (80% strength based on solids content). Based on the solidsfraction (nonvolatile fraction), the amount of IR1 used in I1 was thesame as that of the polyester P1 used in C1. The different amounts ofbutyl glycol arising from the different solid contents of IR1 and ofdispersion P1 were compensated in the formulation I1 by correspondingaddition of butyl glycol.

Preparation of Inventive Basecoat Materials 2 and 3 (I2 and I3)

In the same way as for the preparation of I1, inventive basecoatmaterials I2 and I3 were prepared using the dissolved reaction productsIR2 and IR3. Compensation for the different solids contents in relationto the polyester dispersion P1 took place again by correspondingaddition of butyl glycol.

Table 1 shows again the polyesters and reaction products, and theirproportions (based on the total amount of the waterborne basecoatmaterials), used in waterborne basecoat materials (WBM) C1 and I1 to I3,as an overview.

TABLE 1 Compositions of WBM C1 and I1 to I3 WBM [% by wt.] Reactionproduct C1 4.92 P1 I1 4.92 IR1 I2 4.92 IR2 I3 4.92 IR3

Comparison Between Waterborne Basecoat Materials C1 and I1 to I3

To determine the pinholing limit and pinhole count, multicoat paintsystems were produced by the following general method:

A cathodically electrocoated steel sheet of dimensions 30×50 cm wasprovided with an adhesive strip on one longitudinal edge, in order to beable to determine the film thickness differences after the coating. Theparticular waterborne basecoat material was applied electrostatically inwedge format. The resulting waterborne basecoat film was flashed off atroom temperature for four minutes and subsequently intermediately driedin a forced air oven at 70° C. for 10 minutes. A customary two-componentclearcoat material was applied electrostatically in a film thickness of35 micrometers to the dried waterborne basecoat film. The resultingclearcoat film was flashed off at room temperature for 20 minutes. Thewaterborne basecoat film and the clearcoat film were then cured in aforced air oven at 140° C. for 20 minutes. Following visual evaluationof the pinholes in the resulting wedge-shaped multicoat paint system,the film thickness of the pinholing limit and the number of pinholesabove this film thickness (in other words, the total number of pinholeson the painted sheet) were ascertained. The results can be found intable 2.

TABLE 2 Pinholing limit and pinhole count of multicoat paint systemsproduced using waterborne basecoat materials C1 and I1 to I3 WBMPinholing limit (micrometers) Pinhole count C1 22 25 I1 24 18 I2 26 15I3 29 9

The results emphasize the fact that the use of the reaction products ofthe invention or of the waterborne basecoat materials of the inventionsignificantly increases the pinholing limit by comparison with thecomparative waterborne basecoat material C1, and at the same timereduces the pinhole count.

Production of a Silver Comparative Waterborne Basecoat Material 2 (C2)

The components listed under “aqueous phase” in table B were stirredtogether in the order stated to form an aqueous mixture. In the nextstep an organic mixture was prepared from the components listed under“organic phase”. The organic mixture was added to the aqueous mixture.The combined mixture was then stirred for 10 minutes and adjusted, usingdeionized water and dimethylethanolamine, to a pH of 8 and to a sprayviscosity of 58 mPas under a shearing load of 1000 s⁻¹ as measured witha rotary viscometer (Rheomat RM 180 instrument from Mettler-Toledo) at23° C.

TABLE B Parts by Component weight Aqueous phase 3% Na—Mg phyllosilicatesolution 26 Deionized water 21.7 Butyl glycol 2.8 Polyurethane-modifiedpolyacrylate; 4.5 prepared as per page 7, line 55 to page 8, line 23 ofDE 4437535 A 50% strength by weight solution of 0.6 Rheovis PU 1250(BASF), rheological agent P1 13.3 TMDD (BASF) 0.3 Melamine-formaldehyderesin (Cymel 203 4.1 from Cytec) 10% dimethylethanolamine in water 0.3polyurethane-based graft copolymer; 1.8 prepared as per page 19, line 44to page 20, line 21 of DE 19948004 A, solids content adjusted to 32.5 wt% with deionized water TMDD (BASF) 1.6 3% strength by weight aqueousRheovis 3.9 AS S130 solution; rheological agent, available from BASFOrganic phase Mixture of two commercial aluminum 6.2 pigments, availablefrom Altana-Eckart Butyl glycol 7.5 P1 5

Preparation of Inventive Waterborne Basecoat Materials 4 to 6 (I4 toI16)

In the same way as for the preparation of I1 to I3, inventive basecoatmaterials I4 to I6 were produced using the reaction products IR1 and IR3on the basis of the comparative basecoat material C2 (table B) and withreplacement of the polyester dispersion P1. Compensation for thedifferent solids contents in relation to the polyester dispersion P1took place again by corresponding addition of butyl glycol.

TABLE 3 Compositions of WBM C2 and I4 to I6 WBM [% by wt.] Reactionproduct C2 10.98 P1 I4 10.98 IR1 I5 10.98 IR2 I6 10.98 IR3

Comparison Between Waterborne Basecoat Materials C2 and I4 to I6

As above for the multicoat paint systems produced using waterbornebasecoat materials C1 and I1 to I3, multicoat paint systems wereproduced using aqueous basecoat materials C2 and I4 to I6. Theevaluation in terms of pinholing limit and pinhole count also took placein the same way. The results can be found in table 4.

TABLE 4 Pinholing limit and pinhole count of multicoat paint systemsproduced using waterborne basecoat materials C2 and I4 to I6 WBMPinholing limit (micrometers) Pinhole count C2 14 63 I4 21 23 I5 23 18I6 27 8

The results again emphasize the fact that the use of the reactionproducts of the invention or of the waterborne basecoat materials of theinvention significantly increases the pinholing limit by comparison withthe comparative waterborne basecoat material C2, and at the same timereduces the pinhole count.

1: A pigmented aqueous basecoat material, comprising: acarboxy-functional dimer fatty acid-based reaction product which ispreparable by reaction of (a) at least on dimer fatty acid with (b) atleast one compound of the general structural formula (I):

wherein: R is a C₃ to C₆ alkylene radical; n is selected such that thecompound (b) possesses a number-average molecular weight of 120 to 6000g/mol; components (a) and (b) are used in a molar ratio of at least 1/1;and the reaction product possesses a number-average molecular weight of1000 to 20 000 g/mol and an acid number of 10 to 120 mg KOH/g. 2: Thebasecoat material as claimed in claim 1, wherein the dimer fatty acidcomprises at least 90 wt % of dimeric molecules, less than 5 wt % oftrimeric molecules, and less than 5 wt % of monomeric molecules andother byproducts. 3: The basecoat material as claimed in claim 1,wherein the compound (b) possesses a number-average molecular weight of180 to 2500 g/mol. 4: The basecoat material as claimed in claim 1,wherein the group R in the general structural formula (I) comprisestetramethylene radicals. 5: The basecoat material as claimed in claim 1,wherein components (a) and (b) are used in a molar ratio of 1.1/1 to3/1. 6: The basecoat material as claimed in claim 1, wherein thereaction product possesses a number-average molecular weight of 2500 to10 000 g/mol. 7: The basecoat material as claimed in claim 1, whereinthe reaction product possesses an acid number of 12 to 80 mg KOH/g. 8:The basecoat material as claimed in claim 1, wherein the components (a)and (b) are used in a molar ratio of 1.2/1 to 2/1. 9: The pigmentedaqueous basecoat material as claimed in claim 1, wherein the sum totalof the weight-percentage fractions, based on the total weight of thepigmented aqueous basecoat material, of all the dimer fatty acid-basedreaction products is 0.1 to 30 wt %. 10: The pigmented aqueous basecoatmaterial as claimed in claim 1, further comprising a polyurethane resinthat is grafted by olefinically unsaturated monomers and compriseshydroxyl groups, and a melamine resin. 11: A carboxy-functional dimerfatty acid-based reaction product which is preparable by reaction of (a)at least one dimer fatty acids with (b) at least one compound of thegeneral structural formula (I):

wherein: R is a C₃ to C₆ alkylene radical; n is selected accordinglysuch that the polyether (b) possesses a number-average molecular weightof 120 to 6000 g/mol; components (a) and (b) are used in a molar ratioof at least 1/1; and the resulting reaction product possesses anumber-average molecular weight of 1000 to 20 000 g/mol and an acidnumber of 10 to 120 mg KOH/g. 12: A pigmented aqueous basecoat material,comprising: the reaction product of claim 11, wherein the pigmentedaqueous basecoat material is adapted to function as a basecoat materialfor improving the stability with respect to optical defects in paintsystems. 13: A method for producing a multicoat paint system, the methodcomprising: (1) applying the pigmented aqueous basecoat material ofclaim 1 to a substrate, (2) forming a polymer film from the basecoatmaterial applied in stage (1), (3) applying a clearcoat material to thepolymer film, and then (4) curing the polymer film together with theclearcoat film. 14: The method as claimed in claim 13, wherein thesubstrate is a metallic substrate coated with a cured electrocoat film,and all of the films applied to the electrocoat film are cured jointly.15: A multicoat paint system producible by the method of claim
 13. 16: Amethod for improving stability with respect to optical defects in apaint system, the method comprising: applying a pigmented aqueousbasecoat material comprising the reaction product of claim 11 to asurface to form a basecoat; and painting a surface of the basecoat.